The present invention relates to starch/polymer graft emulsions. More particularly, it relates to the formation of such emulsions using persulfate salts to essentially simultaneously degrade the starch and initiate a polymerization.
It is often desirable to use modified starch polymers for coatings, adhesives, and graphic arts applications. By combining starch with synthetic polymers through graft copolymerization, products with highly desirable combinations of properties can be produced. See e.g. U.S. Pat. Nos. 3,640,925 and 4,171,407. The disclosure of these patents, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
For particular applications, it is highly desirable that certain metallic ions such as iron, nickel, manganese, cerium, and copper not be present as they tend to discolor the resulting products. This is a particular problem for products used in the graphic arts and coating industries for products such as ink binders and coating binders. It is noted, however, that such metals are typically used in starch graft emulsion copolymer systems, either to degrades starch or facilitate the polymerization.
Another issue arises in connection with batch processing of graft polymerization. One set of conditions is often specified for degrading starch (e.g. to modify its viscosity and other characteristics), and another set of conditions is then used for graft polymerization. Changing the reaction conditions can lead to excessive processing times. In addition, often the reactants used in the degradation process are unnecessary or undesirable in the subsequent graft copolymerization.
Thus, it can be seen that a need exists for improved starch stabilized polymeric emulsions, and methods for making them.
The objects of the present invention therefore include providing an emulsion polymer of the above kind:
(a) that has desired viscosity and other characteristics; PA1 (b) which can be made in a process that uses essentially the same conditions for degrading starch as for polymerizing the emulsion; PA1 (c) which uses environmentally acceptable and inexpensive components; and PA1 (d) which is suitable for a wide variety of applications.
These and still other objects and advantages of the present invention will be apparent from the description which follows.